The present invention relates to “pseudo current type 120-degree conduction inverter” and proposes a control apparatus of a motor to drive the motor at the high speed using the pseudo current type 120-degree conduction inverter.
In general, a use of a voltage source PWM inverter for the motor drive apparatus is a major trend. However, in a purpose in which a motor of a class of several kW is driven at a high speed equal to or higher than 100 thousand revolutions per minute, a fundamental wave frequency is as very high as several kHz or more. Therefore, a further higher carrier frequency than the fundamental wave frequency is required to perform a PWM control and, hence, a control is difficult. In addition, in a voltage type 120 degree conduction inverter, current waveforms are worsened during the high-speed drive.
From the above reason, as the apparatus which drives the motor at the high speed, “pseudo current type 120-degree inverter” which performs a PAM control (Pulse Amplitude Modulation control) of an amplitude of an output current and performs a 120 degree conduction control of an output phase has been discussed. A system in which a PM (permanent magnet) motor is controlled by means of the pseudo current type 120-degree conduction inverter has been reported (for example, refer to a non-patent literature 1).
In this system, as shown in a circuit structure example of FIG. 15, a main circuit is constituted by a buck chopper 1 which performs a direct current voltage control and a 120 degree conduction inverter 2 and a control circuit 4 controls buck chopper 1 and inverter 2 so as to enable a high-speed drive for an alternating current motor 3.
In control circuit 4, a detection current of a reactor L of buck chopper 1 in which a direct current voltage is inputted is fed back and switching conductivities of semiconductor switches S1, S2 are controlled to control the direct current voltage of the inverter. A diode 5 returns a high voltage generated at a winding inductance of the motor when the semiconductor switches of inverter 2 are commutated at each of 120 degrees toward a direct current voltage source side.
In addition, control circuit 4 detects three-phase voltages of the motor on the basis of magnetic flux phases of the motor and integrates voltage waveforms of the detected three-phase voltages by an integration circuit having a large time constant to be converted into a magnetic flux phase information (an inner induced voltage phase), this being under a zero cross detection by means of a zero crossing comparator. Then, a logic circuit is intervened to generate a 120 degree conduction pattern synchronized with the inner induced voltage phase of the motor.
As another form of FIG. 15, another pseudo current type 120-degree conduction inverter whose main circuit structure is shown in FIG. 16 or FIG. 17 has been proposed. In FIG. 16, a voltage boost direct current power is obtained by means of a voltage boost circuit 6 in FIG. 16. This structure achieves the inverter using a low voltage direct current power supply such as an on-vehicle battery. In FIG. 17, a rectifying circuit 9 serves to obtain a high-voltage direct current power from a three-phase alternating current power supply and this direct current is controlled by buck chopper 10.    Non-patent literature 1: Japanese publication “pp. 854-861, No. 9, Electric Engineering Society of Japan titled 220000-r/min, 2-kW PM Motor Drive for Turbocharger”.